The proposed project is designed to study the morphological, biochemical, and immunological aspects of the mouse mammary tumor virus (MTV or B particles) as well as of A particles, which are considered as the precursors of B particles. We plan to isolate the subviral components of A and B particles by disrupting the particles with detergent and subsequent fractionation by density gradient centrifugation. The homogeneity and morphological features of the subviral components will be monitored by electron microscopy. Purified fractions as well as intact particles will be subjected to polyacrylamide gel electrophoresis; it is anticipated that a comparison between the the protein composition of the viral components and the intact virus will enable us to determine the location of the various proteins of MTV within its structural components. Particular emphasis will be given to the investigation of the relationships between the various proteins of MTV and of A particles in order to understand the morphogenesis of MTV. This aim is hoped to be accomplished by isolating the proteins of MTV and of A particles using analytical procedures, producing antisera against them and analysing the reactivity of these reagents through various immunological techniques. We also plan to isolate the MTV and A particle reverse transcriptases making use of the affinity chromatographic method which we have developed and have found very effective in purifying the reverse transcriptases from other oncornaviruses. A thorough study of the biochemical and immunological properties of the viral reverse transcriptases also should provide valuable information concerning the relationships between A and B particle morphogenesis. Antisera against the purified viral reverse transcriptases will be extremely useful as a diagnostic reagent in search of MTV related information in human breast cancer.